feat: add /history switch for runtime database backend switching

Add log_database_switch_backend() that closes the current backend,
updates PREF_DBLOG preference, and reinitializes with the new backend
without requiring a reconnect or restart.

New command: /history switch sqlite|flatfile
- Validates connection state and backend name
- Skips if already using the requested backend
- Autocomplete support for the subcommand

src/command/cmd_ac.c

@@ -276,6 +276,7 @@ static Autocomplete logging_group_ac;
 static Autocomplete privacy_ac;
 static Autocomplete privacy_log_ac;
 static Autocomplete history_ac;
+static Autocomplete history_switch_ac;
 static Autocomplete color_ac;
 static Autocomplete correction_ac;
 static Autocomplete avatar_ac;
@@ -431,6 +432,7 @@ static Autocomplete* all_acs[] = {
     &privacy_ac,
     &privacy_log_ac,
     &history_ac,
+    &history_switch_ac,
     &color_ac,
     &correction_ac,
     &avatar_ac,
@@ -1144,10 +1146,14 @@ cmd_ac_init(void)
 
     autocomplete_add(history_ac, "on");
     autocomplete_add(history_ac, "off");
+    autocomplete_add(history_ac, "switch");
     autocomplete_add(history_ac, "verify");
     autocomplete_add(history_ac, "export");
     autocomplete_add(history_ac, "import");
 
+    autocomplete_add(history_switch_ac, "sqlite");
+    autocomplete_add(history_switch_ac, "flatfile");
+
     autocomplete_add(logging_group_ac, "on");
     autocomplete_add(logging_group_ac, "off");
     autocomplete_add(logging_group_ac, "color");
@@ -1795,6 +1801,11 @@ _cmd_ac_complete_params(ProfWin* window, const char* const input, gboolean previ
         }
     }
 
+    result = autocomplete_param_with_ac(input, "/history switch", history_switch_ac, TRUE, previous);
+    if (result) {
+        return result;
+    }
+
     result = autocomplete_param_with_ac(input, "/history", history_ac, TRUE, previous);
     if (result) {
         return result;

src/command/cmd_defs.c

@@ -1882,17 +1882,20 @@ static const struct cmd_t command_defs[] = {
               CMD_TAG_CHAT)
       CMD_SYN(
               "/history on|off",
+              "/history switch sqlite|flatfile",
               "/history verify [<jid>]",
               "/history export [<jid>]",
               "/history import [<jid>]")
       CMD_DESC(
               "Switch chat history on or off, /logging chat will automatically be enabled when this setting is on. "
               "When history is enabled, previous messages are shown in chat windows. "
+              "Use 'switch' to change the active database backend at runtime without reconnecting. "
               "Use 'verify' to check integrity of stored message history. "
               "Use 'export' to copy messages from SQLite to flat-file format, or 'import' to copy from flat-file to SQLite. "
               "Both export and import merge with existing data (duplicates are skipped).")
       CMD_ARGS(
               { "on|off", "Enable or disable showing chat history." },
+              { "switch sqlite|flatfile", "Switch the active database backend at runtime." },
               { "verify [<jid>]", "Verify integrity of message history. Optionally specify a JID to check only one contact." },
               { "export [<jid>]", "Export SQLite history to flat-file format. Optionally specify a JID to export only one contact." },
               { "import [<jid>]", "Import flat-file history into SQLite. Optionally specify a JID to import only one contact." })

src/command/cmd_funcs.c

@@ -6735,6 +6735,37 @@ cmd_history(ProfWin* window, const char* const command, gchar** args)
         return TRUE;
     }
 
+    if (g_strcmp0(args[0], "switch") == 0) {
+        jabber_conn_status_t conn_status = connection_get_status();
+        if (conn_status != JABBER_CONNECTED) {
+            cons_show_error("You must be connected to switch database backend.");
+            return TRUE;
+        }
+
+        if (args[1] == NULL) {
+            cons_bad_cmd_usage(command);
+            return TRUE;
+        }
+
+        if (g_strcmp0(args[1], "sqlite") != 0 && g_strcmp0(args[1], "flatfile") != 0) {
+            cons_show_error("Backend must be 'sqlite' or 'flatfile'.");
+            return TRUE;
+        }
+
+        if (active_db_backend && g_strcmp0(active_db_backend->name, args[1]) == 0) {
+            cons_show("Already using '%s' backend.", args[1]);
+            return TRUE;
+        }
+
+        cons_show("Switching database backend to '%s'...", args[1]);
+        if (log_database_switch_backend(args[1])) {
+            cons_show("Database backend switched to '%s'.", args[1]);
+        } else {
+            cons_show_error("Failed to switch database backend.");
+        }
+        return TRUE;
+    }
+
     if (g_strcmp0(args[0], "verify") == 0) {
         const gchar* contact_jid = args[1]; // may be NULL (verify all)
         cons_show("Verifying history integrity...");

src/database.c

@@ -44,6 +44,7 @@
 #include "config.h"
 #include "database.h"
 #include "config/preferences.h"
+#include "config/accounts.h"
 #include "ui/ui.h"
 #include "xmpp/xmpp.h"
 #include "xmpp/message.h"
@@ -96,6 +97,34 @@ log_database_close(void)
     active_db_backend = NULL;
 }
 
+gboolean
+log_database_switch_backend(const char* new_backend)
+{
+    // Close current backend
+    log_database_close();
+
+    // Update preference
+    prefs_set_string(PREF_DBLOG, new_backend);
+    prefs_save();
+
+    // Get current account to reinitialize
+    const char* account_name = session_get_account_name();
+    if (!account_name) {
+        log_error("log_database_switch_backend: no active session");
+        return FALSE;
+    }
+
+    ProfAccount* account = accounts_get_account(account_name);
+    if (!account) {
+        log_error("log_database_switch_backend: account '%s' not found", account_name);
+        return FALSE;
+    }
+
+    gboolean result = log_database_init(account);
+    account_free(account);
+    return result;
+}
+
 void
 log_database_add_incoming(ProfMessage* message)
 {

src/database.h

@@ -93,6 +93,7 @@ db_backend_t* db_backend_flatfile(void);
 
 // Public API (dispatches to active_db_backend)
 gboolean log_database_init(ProfAccount* account);
+gboolean log_database_switch_backend(const char* new_backend);
 void log_database_add_incoming(ProfMessage* message);
 void log_database_add_outgoing_chat(const char* const id, const char* const barejid, const char* const message, const char* const replace_id, prof_enc_t enc);
 void log_database_add_outgoing_muc(const char* const id, const char* const barejid, const char* const message, const char* const replace_id, prof_enc_t enc);

tests/unittests/database/stub_database.c

@@ -25,9 +25,14 @@
 
 #include "config.h"
 #include "database.h"
+#include "database_flatfile.h"
 
 db_backend_t* active_db_backend = NULL;
 
+// The flatfile parser needs this global for path construction.
+// In tests we keep it NULL since no real file I/O happens via the backend.
+char* g_flatfile_account_jid = NULL;
+
 gboolean
 log_database_init(ProfAccount* account)
 {
@@ -53,6 +58,11 @@ void
 log_database_close(void)
 {
 }
+gboolean
+log_database_switch_backend(const char* new_backend)
+{
+    return TRUE;
+}
 GSList*
 log_database_verify_integrity(const gchar* const contact_barejid)
 {